In recent years, development of a display technology called a see-through display (transparent display) that not only an image is displayed on a screen but also an object on the background of the display can be visually recognized through the screen has been actively promoted. In order to achieve a see-through display, various approaches have been proposed such as an approach in which a liquid crystal panel or an organic EL (Electro-Luminescence) panel is used. For example, a display described in Patent Document 1 includes a translucent panel and a transmittance varying unit disposed on a back surface side of the panel to face the panel. When an image and a character are displayed on a display screen of this panel, transmittance of a character area including the character displayed on the display screen in the transmittance varying unit is set to be higher than transmittance of an image area including the image. This suppresses decrease in visibility of a display content. Further, Patent Document 2 describes a display that adjusts luminance of light from a backlight, when external brightness changes, based on illuminance measured by an illuminance sensor.